Heterosis in age-specific selected populations of a seed beetle: Sex
differences in longevity and reproductive behavior

2015

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We tested mutation accumulation hypothesis for the evolution of
senescence using short-lived and long-lived populations of the
seed-feeding beetle, Acanthoscelides obtectus (Say), obtained by
selection on early-and late-life for many generations. The expected
consequence of the mutation accumulation hypothesis is that in
short-lived populations, where the force of natural selection is the
strongest early in life, the late-life fitness traits should decline due
to genetic drift which increases the frequency of mutations with
deleterious effects in later adult stages. Since it is unlikely that
identical deleterious mutations will increase in several independent
populations, hybrid vigor for late-life fitness is expected in offspring
obtained in crosses among populations selected for early-life fitness
traits. We tested longevity of both sexes, female fecundity and male
reproductive behavior for hybrid vigor by comparing hybrid and nonhybrid
short-lived populations. Hybrid vigor was confirmed for male virility,
mating speed and copulation duration, and longevity of both sexes at
late ages. In contrast to males, the results on female fecundity in
short-lived populations did not support mutation accumulation as a
genetic mechanism for the evolution of this trait. Contrary to the
prediction of this hypothesis, male mating ability indices and female
fecundity in long-lived populations exhibited hybrid vigor at all
assayed age classes. We demonstrate that nonhybrid long-lived
populations diverged randomly regarding female and male reproductive
fitness, indicating that sexually antagonistic selection, when
accompanied with genetic drift for female fecundity and male virility,
might be responsible for overriding natural selection in the
independently evolving long-lived populations.